1. Field of the Invention
The present invention relates to a fuel injection apparatus for an internal combustion engine, and more specifically to a setting device of basic fuel injection amount for an internal combustion engine.
2. Description of the Related Art
An example of a conventional electronically controlled setting device of fuel injection amount for an internal combustion engine is given in Japanese Patent Publication of Unexamined Application No. SHO-59-203828 in which the operation of a fuel injection valve is controlled based on the basic amount of fuel injection preset corresponding to the operating status of the engine, specifically, on the amount of fuel injected corresponding to the amount of intake air for one revolution of the engine.
In this conventional device, the basic amount of injected fuel Tp (=K.times.Q/N, where K is a constant) is calculated from the amount Q of intake airflow detected by an airflow meter and the engine velocity N detected by an ignition signal etc. After calculation of the various revision coefficients (COEF) corresponding to the engine operating status determined from the cooling water temperature and so on, the revision coefficient .alpha. from the feedback of the air/fuel ratio, and the revised portion Ts from the battery voltage, the amount of Ti of fuel injected is calculated according to the equation: EQU Ti=Tp.times.COEF.times..alpha.+Ts
Then an injection pulse signal of the pulse width corresponding to the calculated amount Ti of fuel injection is output, so that the prescribed amount of fuel is injected into the engine.
In addition, the ignition timing of the spark plug is calculated from the basic amount Tp of fuel injection calculated and the engine velocity N.
Incidentally, one problem with the above-mentioned conventional electronically controlled fuel injection device for an internal combustion engine is that, as shown in FIG. 7, in the fuel injection during the initial stage of the acceleration of the engine, an amount of intake air detected by the airflow meter is inclined to be smaller than the amount of air actually taken into the cylinder because of the delay in response of the detected amount of intake airflow and the delay in calculation by the control device. If the basic amount of fuel injection is preset based on this detected amount of intake airflow, the basic amount of fuel injection preset is smaller than the amount actually required by the engine, causing an overleaning of the air/fuel ratio. On the other hand, in the final stage of the acceleration, an amount of intake air detected is larger than the actual amount of intake air because the amount of air detected by the airflow meter includes the portion of the air which fills the intake manifold, specifically, the amount of air which fills the intake manifold and does not enter the cylinder, and consequently the air/fuel ratio becomes overrich.
Then, in the initial acceleration period, an amount of fuel injected into the engine is inclined to be smaller than that required by the engine, which causes an overlean air/fuel ratio. This causes the problems of acceleration shock, worsening of the situation of the exhaust gases (an increase in the discharge of nitrogen oxides, NOx), the occurrence of knocking and so on.